Induction heating system

ABSTRACT

An induction heating system which utilizes a U-shaped magnetic core with the end surfaces of the legs of the core being placed in engagement with the base of a fastener device adapted to be adhesively mounted to a workpiece to be heated to form a closed magnetic circuit with the base. The end surfaces of the legs are formed at an angle to the axis of the legs to allow the magnetic circuit to be completed directly beneath a stud member extending peripherally to the base to activate adhesive beneath the stud and adhere the fastener device to a workpiece.

United States Patent [1 1 McBriarty [111 3,883,712 [4 May 13, 1975 INDUCTION HEATING SYSTEM [75] Inventor: Robert Burke MclBriarty, Elgin, Ill.

[73] Assignee: Illinois Tool Works Inc., Chicago,

Ill.

22 Filed: Oct.l,l973

21 Appl. No.: 398,718

[52] US. Cl. 2l9/l0.79; 219/9.5; 219/10.53 [51] Int. Cl. I-IOSb 5/08 [58] Field of Search 219/10.79, 10.41, 10.43,

[56] References Cited UNITED STATES PATENTS 1,996,502 4/1935 Brown 219/l0.79 2,184,282 12/1939 Capita 219/10.79 2,367,927 1/1945 Chubb 336/216 X 2,430,285 11/1947 Ferris 2l9/10.79 2,761,941 9/1956 Ardichvili 219/10.49 2,785,263 3/1957 Van lperen 2l9/l0.79

2,873,344 2/1959 Kocks et a1. 2l9/l0.79 3,268,704 8/1966 Cornwell 2l9/lO.6l

3,719,792 3/1973 Cuccaro 219/230 3,816,690 6/1974 Mittleman 2l9/l0.75

Primary Examiner-Bruce A. Reynolds Attorney, Agent, or FirmRobert W. Beart; Thomas W. Buckman [5 7 ABSTRACT An induction heating system which utilizes a U-shaped magnetic core with the end surfaces of the legs of the core being placed in engagement with the base of a fastener device adapted to be adhesively mounted to a workpiece to be heated to form a closed magnetic circuit with the base. The end surfaces of the legs are formed at an angle to the axis of the legs to allow the magnetic circuit to be completed directly beneath a stud member extending peripherally to the base to activate adhesive beneath the stud and adhere the fastener device to a workpiece.

4 Claims, 5 Drawing Figures INDUCTION HEATING SYSTEM The present invention relates to an improved magnetizable core useful in heating an adhesive fastener device for attachment to a workpiece.

The improved core design disclosed herein is especially useful with fastener devices which include a stud projecting from a base member which carries heat activable adhesive on the underside thereof.

Examples of fasteners with which the present invention may be advantageously used are those shown in U.S. Pat Nos. 3,719,792 and 3,593,001. The adhesive used with these fasteners is shown to be activated by resistance heating methods and not induction heating methods and more specifically the prior art systems do not use the theory of the completion of a magnetic circuit through the workpiece to be heated to generate heat in the workpiece. Conventional cores and methods of utilizing this advantageous heating method would not allow the legs of a U-shaped core to be positioned in such a manner as to concentrate the heat directly beneath the axis or intersecting the axis of the stud. Prior art heating systems, such as that shown in U.S. Pat. Nos. 2,761,941 and 2,785,263, obviously would not allow the positionment of the legs of the core in such a manner as to heat directly beneath the axis of a stud since the bridge of the core would interfere with a stud which is longer than the legs of the core. An obvious manner of heating such fasteners with conventional U-shaped cores would be to lengthen the legs of the cores so that the bridge may be positioned above the free extremity of the stud. This has the disadvantage of loss of efficiency in heating due to the heat losses that would be encountered in the core itself due to the very large length of the legs.

The present invention generally provides a design for a U-shaped core which is capable of being positioned on a fastener, which includes a stud portion and an adhesive carrying base portion, in such a manner as to direct the flux path of induced current through the base in a path which generally intersects the axis of the stud portion. This will allow the heat to be concentrated directly beneath and in line with the stud and, therefore, act on the adhesive in the most critical area. This particular advantageous heating procedure is achieved by the novel structure of the U-shaped core. The ends of the legs of the core are formed of end surfaces which are inclined to the axis of the legs. This will allow the end surfaces to be positioned on either side of the axis of the stud, without an appreciable air gap between the core and the base of the fastener, and thus position the bridge of the core laterally of the stud. This design will thus allow a fastening device with a relatively long stud portion to be heated as effectively and efficiently as a fastener which has a generally short stud portion.

One of the important objects of the invention is, therefore, to provide a U-shaped core which can be used to heat the base of an adhesive fastener of a variety of lengths of studs.

Another object of the invention is to provide a U- shaped magnetizable core which directs a flux path through the base of a fastener and which flux path intersects the axis of a stud extending perpendicularly to the base.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of the core as it is used to generate heat in an associated fastener.

FIG. 2 is a side view of the system shown in FIG. 1.

FIG. 3 is a top view of the system shown in FIGS. 1 and 2 FIG. 4 is a plan view of a generally annular laminated winding from which two cores can be formed.

FIG. 5 is an elevation view of the winding shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now the drawings, reference numeral 10 denotes the U-shaped magnetizable core member which is the subject matter of the invention. Core 10 includes a pair of legs 14 extending at right angles to a bridge portion 12 interconnecting these legs. As shown in FIG. 2, the axes of the bridge and leg portions are generally coplanar and the terminal surfaces 16 of the legs are formed at an acute angle to the axis of the legs, for a purpose to be described hereinafter.

FIGS. 1, 2 and 3 of the drawings show the core 10 in operative position to heat the base of an associated fastener member 20. The fastener 20 includes a base portion 24 having a generally planar upper and lower surface and, as shown in the drawings, may be of a square or rectangular configuration. A stud member 22 extends perpendicularly to the base and the underside of the base is provided with a heat activable adhesive layer 26. When the adhesive is subjected to the proper heat level, it provides a bond between the base portion 24 and a secondary workpiece or support surface 28. A fastener thus applied to a support surface will thereafter provide a means for attachment of other devices to the support surface 28 without requiring surface preparation, such as provision of holes, and without requiring access to both sides of the support surface. As will be understood, the fastener unit 20, may be of a variety of specific configurations within the above mentioned general configuration and the stud portion 22 may be of any mechanical fastening means extending from the base of the fastener. The stud 22 may be of a variety of lengths.

The novel configuration of the core 10 is particularly useful and advantageous to heat the adhesive directly beneath the base and in a path which generally intersects the axis of the stud 22. As can be readily apparent from FIGS. 1 and 2, the angularly disposed end surfaces 16 allow the legs of the core to be positioned on the base and on either side of the stud 22 and eliminates the interference between the bridge 12 of the core and a stud having a length greater than the length of the legs, since the bridge will be disposed laterally of the stud 22. The magnetic circuit induced in the core by coil 18, looped around the bridge, is thus free to be completed through the base of the fastener 24 in a path which generally intersects the center line of the stud. The adhesive is thus heated and cured most efficiently in the path directly beneath the stud.

When a U-shaped core is used to heat a workpiece by the completion of a magnetic path between the legs of the core, it is important to maximize the heat losses in the workpiece and not create heat in the core itself. For this reason, it is important that the legs 14 be of a limited length. The end surfaces of the legs must be in close physical contact with the base or workpiece to be heated so that the flux may be channeled directly through the workpiece without allowing an appreciable amount of flux leakage from the intended path and thus heat the base by hysteresis loss and eddy currents.

It has been found that end surfaces disposed in the same plane which extends approximately 30 to the axis of the legs are adequate to heat the base of a fastener in a path which intersects the axis of the stud and yet dispose the bridge of the core laterally of a stud, since this relationship will position the legs at an angle of 60 to the base as shown in FIG. 2.

It is desirable to manufacture the U-shaped core of a laminated structure to insure that the losses occur primarily in the workpiece rather than in the core. Turning to FIGS. 4 and 5, a preferred method of manufacturing the core of the present invention is shown. Several layers or laminations of suitable core sheet material are wound about a mandrel having a cross-sectional configuration represented by reference numeral 32 in FIG. 4. The laminations will have a width determined by the desired width of the legs 14 and, of course, the thickness of the leg is detennined by the number of laminations provided. After the winding 30 is completed, the generally annular shaped core is severed at cut lines 36 which extend to an angle 30 to a plane extending at right angles to the winding. Since cut lines are made at an axis of symmetry of the annular coil, the coils produced will be identical.

While the invention has been described with particular reference to a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A U-shaped induction heating core for use in activating adhesive in a heat activable adhesive fastener member, such as a stud with an adhesive carrying base extending generally to the axis of the stud, the core including a pair of parallel legs interconnected by a bridge section extending substantially perpendicular to the legs, the bridge section and legs having substantially rectangular cross-sectional configurations with the axes of the bridge and legs lying in in the same plane, the free terminal extremity of each leg forming substantially flat, planar end surfaces which are coplanar with each other, and therefore adapted for intimate contact with the base of a fastener so that flux may be channeled directly through the base without allowing an appreciable amount of flux leakage, the planar end surfaces being disposed at an acute angle to the plane which includes the axes of the bridge and legs, and therefore presents end surface areas greater than the cross-sectional area of the legs, wherein a magnetic flux path created in the core through the use of a current carrying coil wound thereabout may be minimized thus minimizing the core losses while allowing the flux path to be completed through the base of the fastener member directly beneath the axis of the stud.

2. A magnetic core in accordance with claim 1, comprising a plurality of laminations of magnetic material parallel to said first plane.

3. A magnetic core in accordance with claim 1, comprising a pair of legs each extending 90 to the bridge portion.

4. An induction heating system in accordance with claim 1, wherein the end surfaces of the legs are disposed at an angle of 30 to the plane which includes the axes of the bridge and the legs. 

1. A U-shaped induction heating core for use in activating adhesive in a heat activable adhesive fastener member, such as a stud with an adhesive carrying base extending generally 90* to the axis of the stud, the core including a pair of parallel legs interconnected by a bridge section extending substantially perpendicular to the legs, the bridge section and legs having substantially rectangular cross-sectional configurations with the axes of the bridge and legs lying in in the same plane, the free terminal extremity of each leg forming substantially flat, planar end surfaces which are coplanar with each other, and therefore adapted for intimate contact with the base of a fastener so that flux may be channeled directly through the base without allowing an appreciable amount of flux leakage, the planar end surfaces being disposed at an acute angle to the plane which includes the axes of the bridge and legs, and therefore presents end surface areas greater than the cross-sectional area of the legs, wherein a magnetic flux path created in the core through the use of a current carrying coil wound thereabout may be minimized thus minimizing the core losses while allowing the flux path to be completed through the base of the fastener member directly beneath the axis of the stud.
 2. A magnetic core in accordance with claim 1, comprising a plurality of laminations of magnetic material parallel to said first plane.
 3. A magnetic core in accordance with claim 1, comprising a pair of legs each extending 90* to the bridge portion.
 4. An induction heating system in accordance with claim 1, wherein the end surfaces of the legs are disposed at an angle of 30* to the plane which includes the axes of the bridge and the legs. 